FIG. 1 is across sectional view of a conventional loudspeaker system. In the figure, a reference numeral 51 denotes a frame member made of a metal plate, 52 denotes an upper plate, 52a denotes a dowel (projection) formed on the upper plate 52, 53 denotes a pole-piece, and 54 denotes a magnet. A reference numeral 55 denotes a bobbin, 55a denotes a voice coil fixed in a state of being wound around the bobbin 55, 56 denotes a gasket, 57 denotes a mounting screw, 58 denotes a vibrating plate, and 58a denotes a center cap of the vibrating plate 58. A reference numeral 59 denotes an edge, 60 denotes a damper section, 61 denotes a terminal block, 62 denotes a terminal, 63 denotes a gold string wire, and 64 denotes an air gap. FIG. 2 is a plan view of construction of the frame member 51 shown in FIG. 1. In the figure, 51a denotes eight windows arranged in a circle, 51b denotes a central hole for use in accommodating the voice coil 55a, and 51c denotes four holes for use in allowing insertion of the dowel 52a of the upper plate 52. A reference numeral 51d denotes four holes for use in allowing insertion of the mounting screws 57, 51e denotes a notch, and 51f denotes a long hole.
When the conventional loudspeaker system is assembled, the four dowels 52a of the upper plate 52 are inserted into the four holes 51c of the frame member 51, and then their tops of the dowels 52a are crushed (swaged) due to plastic deformation processing. In this way, the frame member 51 is held to the upper plate 52. The magnet 54 is sandwiched and fixed between the upper plate 52 and the pole-piece 53 due to adhesive. An inner periphery of a central hole of the disc-shaped damper section 60 is bonded to the bobbin 55, and an outer periphery of the damper section 60 is bonded to the frame member 51. An inner periphery of a central hole of the vibrating plate 58 is also bonded to the bobbin 55, and an outer periphery of the vibrating member 58 is bonded to the frame member 51 through the edge 59. The center cap 58a is mounted to a central section of the vibrating member 58. A cylindrical-shaped bobbin 55 around which the voice coil 55a is wound is movably inserted into the air gap 64 as a gap defined between a rod-shaped pole of the pole-piece 53 and a hole of the upper plate 52. Moreover, the terminal 62 is fixed to the terminal plate 61 due to a grommet and so on, and a lead wire supplying electric signals to the terminal 62 is soldered thereto.
Next, an operation will be explained.
Electric signals (acoustical signals) inputted to the terminal 62 is supplied to the voice coil 55a through the gold string wires 63. The voice coil 55a produces a magnetic flux in response to the electric signals and a mechanical displacement due to the interaction with a magnetic circuit including the upper plate 52, the pole-piece 53 and the magnet 54. In other words, the bobbin 55 integrated with the voice coil 55a vibrates (in up-and-down directions on a paper of FIG. 1) in response to the supplied electric signals. The vibrating plate 58 vibrates due to the vibration of the voice coil 55a, and produces sound due to change in air pressure based on the vibration.
The damper section 60 has the function of braking free vibration of the vibrating plate 58. The eight windows 51a arranged in the frame member 51 have the function of releasing air pressure, which is generated between the vibrating plate 58 and the frame member 51 due to the vibration of the voice coil 55a, to outside. When the damper section 60 brakes improperly the free vibration of the vibrating plate 58, unclear-cut sound is produced. When the windows 51a are not formed, small sound is produced. Therefore, an area of the window 51a of the frame member 51 exerts direct influence upon sound quality and level. With the metal frame member 51 shown in FIG. 2, the windows 51a are formed due to presswork.
Furthermore, the notch 51e and the long hole 51f have the function of absorbing a mechanical distortion, which occurs when the loudspeaker system is mounted. For example, when the loudspeaker system is mounted on an unevenness location in a vehicle, portions enclosing the notch 51e and the long hole 51f are deformed on securing with screws to contain the distortion of the frame member 51 in a local periphery of the hole 51d. Therefore, an axis of the voice coil 55a is kept precisely without deviating from a center of rotation.
Since the conventional loudspeaker system is constructed as described above, it has the following problems.
Firstly, there are defects of the metal frame member that the frame member 51 has a tendency to produce a self-resonance when the vibrating plate 7 in response to the acoustic signals and that a self-resonance frequency enters into the audio-frequency region. Since the self-resonance occurs due to vibration out of the outside of the loudspeaker system, the frame member has a tendency to especially produce the self-resonance when the system is mounted on the vehicle.
For example, with 13 cm-bore loudspeaker system using a frame member made of aluminum plate in 0.7 mm thickness, a self-resonance frequency of the frame member is concentrated close to 1.5 kHz as audible frequencies. Therefore, since sounds generated due to the self-resonance of the frame member is mixed to sound produced due to the vibrating plate, there is a problem that sound quality is impaired remarkably.
As measures against the impairment of the sound quality, there is the idea of increasing the weight of the frame member. For example, since a zinc-casting frame member can prevent its self-resonance from exerting an influence upon sound quality, it is used especially to a large loudspeaker system for home and commercial use. Moreover, a press-worked frame member made of a thickened metal plate also can prevent its self-resonance from exerting an influence upon sound quality.
However, since expensive press machines and stamping dies need for press-working the metal frame member, there is a problem that the cost of manufacturing is inherently high. There is a problem that the zinc-casting frame member results in further increasing the cost of manufacturing because of needs for many stages in secondary processing to obtain the frame member in a required form. Moreover, there is a problem that the thickened metal frame member results in increasing the cost of manufacturing due to materials cost.
Furthermore, when the weight of the frame member is increased, the shape of the loudspeaker system becomes larger. Especially, when the system is mounted on a vehicle, it is difficult to mount the system thereon because of the limit of space for mounting the system thereon. Moreover, when many systems having the frame member weighed are mounted thereon, the design cannot be adopted because of increasing the weight of the vehicle.
Secondarily, the metal frame member is made of quite iron material in respects of materials cost and machinability. Since the iron-made frame member is however ferromagnetic substance, there is a problem of reducing efficiency because of magnetic flux leaked from magnetic circuits.
Third, there are defects of the metal frame member that the cost of discarding and disposing rises due to environmental protection when the loudspeaker system is disposed because of replacement or breakage of parts. In order to protect environment when industry products are disposed generally, ways for reuse or recycle and disposition without environmental destruction are considered. With the loudspeaker system, it is difficult to recycle the system under present circumstances, and a majority of parts in the system is disposed. On disposition of the parts, there is a need to divide the system into parts.
With one example of the loudspeaker system shown in FIG. 1, the frame member 51 is however held to the upper plate 52 due to swaging. Therefore, it is very difficult to carry out divisional works and it takes much time to do it. Expenses involved in the divisional works, labor costs and working time result in increasing the cost of disposition. This becomes an economical factor that leads up to increasing of the cost of new products or a vicious cycle.
On the other hand, in order to facilitate separation between the parts of the system, there is the idea of using the frame member made from resin-forming materials. Under the current household electrical appliance recycling law, since the resin materials is out of target for recycling, divided resin materials are wasted in soil. The resin materials are not decomposed semi-permanently because a secular variation of the resin materials in soil and water is smaller than that of metal materials. There are problems of not protecting environment.
Fourthly, the metal and resin-made frame member possesses high stiffness. With the loudspeaker system for use in being mounted on the vehicle, there are problems that it is difficult to perform mounting works because the system is mounted on an evenness face and because impediments such as various kinds of projections are arranged at locations where the system is mounted.
The invention was made to solve the foregoing problems. Accordingly, it is an object of the invention to provide a loudspeaker system having the outstanding acoustic characteristics without loss of sound quality because of self-resonance of the frame member occurred due to vibration of the vibrating plate.
A further object of the invention is to provide an inexpensive loudspeaker system manufactured at a low cost.
A still further object of the invention is to provide an efficiency-enhancing loudspeaker system reducing magnetic flux leaked from magnetic circuits to the frame member.
An another object of the invention is to provide a cost-reduction loudspeaker system, which facilitates to separate from parts when the loudspeaker system is disposed.
A further object of the invention is to provide a high endurance loudspeaker system usable during a long period of time, the system reducing discarding frequency to protect environments.
A still further object of the invention is to provide a loudspeaker system facilitating performing mounting works.
An another object of the invention is to provide a loudspeaker system having a high degree of flexibility in design of the system.
A further object of the invention is to provide a loudspeaker system solving various kinds of problems concerned with respect to use of a paper frame member.